Developing effective treatments of malignant tumors is still a challenge, despite encouraging progress during the last decades. Today, the most commonly used treatment for advanced metastasized cancer involves the use of cytostatic drugs, sometimes one or more in combination. Cytostatic drugs affect proliferating cells by interfering with fundamental processes of cell multiplication, thereby inducing cell arrest or cell death. Targets include DNA, nucleotide metabolism, enzymes related to DNA integrity, and the cytoskeleton. A group of cytostatic drugs proven to be effective in the treatment of cancer comprises alkylating agents, antimetabolites, inhibitors of mitosis, cytostatic antibiotics, platinum based compounds and topoisomerase inhibitors.
Superantigens are bacterial, viral proteins, and now, human-engineered molecules, capable of activating T lymphocytes at picomolar concentrations. They bind directly to the major histocompatibility complex (MHC) without being processed. Superantigens bind unprocessed outside the antigen-binding groove on MHC class II molecules, thereby avoiding most of the polymorphism in the conventional peptide-binding site. Superantigens bind to the Vβ chain of the T cell receptor (TCR), instead of binding to the hypervariable loops of the T cell receptor (TCR) and activate T cells. Therefore, when a superantigen is administered to an animal, such as a human, a subset of T cells is non-specificially activated by the superantigen, as opposed to administration of a “regular” antigen, which would specificially activate only a small sub-set of T cells. Examples of bacterial superantigens include, but are not limited to, Staphylococcal enterotoxin (SE), Streptococcus pyogenes exotoxin (SPE), Staphylococcus aureus toxic shock-syndrome toxin (TSST-1), Streptococcal mitogenic exotoxin (SME), Streptococcal superantigen (SSA), Staphylococcal enterotoxin A (SEA), and Staphylococcal enterotoxin E (SEE).
As discussed in more detail below, and in the U.S. patent applications and patents noted and incorporated herein by reference, superantigens can be modified, for example, by modifying the DNA sequences encoding superantigens, such that, for example, they encode modified superantigens having improved therapeutic properties. For example, modified superantigens can have reduced binding to MHC class II antigens compared to unmodified wild-type superantigens, resulting in reduced systemic toxicity, and/or can have reduced seroreactivity and/or decreased ability to induce an antibody response compared to the wild-type superantigens, resulting in reduced encounters with, and potential difficulties with, host antibodies. An example of a modified superantigen is SEA/E (e.g., SEA/E-120), described in detail below, which binds to MHC class II antigens to activate T cells (e.g., like that of wild-type SEA), and has reduced seroreactivity (e.g., lower than wild-type SEE).
In some embodiments of the present invention, a targeting moiety, for example an antibody or antibody fragment, may be conjugated to a superantigen (wild-type or modified), providing a targeted superantigen. If the antibody, or antibody fragment recognizes a tumor-associated antigen, the targeted superantigen may be called a tumor-targeted superantigen (“TTS”). Targeted superantigens retain the ability to activate large number of T lymphocytes, and add the ability to direct the activated lymphocytes to cells bearing the target moiety. For example, TTS molecules activate large numbers of T cells and direct them to tissues containing the tumor-associate antigen that is recognized by the targeting moiety. By doing so, specific target cells can be killed, leaving the rest of the body relatively unharmed. Such “magic bullet” therapy is quite desired in the art, as non-specific anticancer agents, such as radiation, and cytostatic and cytotoxic chemotherapeutic drugs, are nonspecific and kill large numbers of cells that are not associated with tumors to be treated. For example, studies with TTS have show that inflammation by cytotoxic T lymphocytes (CTLs) into tumor tissue increases rapidly in response to the first injection of a targeted superantigen (Dohlsten et al., 1995). This inflammation with infiltration of CTLs into the tumor is one of the major effectors of the anti-tumor therapeutic of targeted superantigens.
Anticancer agents, such as cytostatic drugs and radiation, generally work by affecting or preventing cell division. Because they are nonspecific, for example, all dividing cells in a treated animal, such as a human, are affected. This typically results in extreme adverse side effects from chemotherapy treatment, such as gastrological disturbances, loss of hair, and damage to the immune system, that are notoriously well-known, both to those skilled in the art as well as to the population as a whole.
Many aspects of the immune system is characterized by dividing cells. For example, in an immune response, the requisite immunocyte expansion phase is characterized by immune cell proliferation. This proliferation is fundamental and essential to a productive immune response. Since cytostatic agents affect dividing cells, cytostatic agents are known to be deleterious to the immune system. In fact, a compromised immune system is one of the more common and serious side effects of treating cancer with chemotherapeutic drugs.
On the other hand, immune therapy relies on a functional immune system. (Chen 2003; Le Poole et al., 2003). Immune therapies such as tumor vaccines rely on a functional immune response in a treated patient. For example, for a productive immune response to a tumor vaccine, T and B lymphocytes must be activated, expand and differentiate into sufficient numbers of effector cells (Le Poole et al., 2003; Chen 2003). This of course requires cell division. Further, it is highly probable that such an immune response also requires that the immunocyte proliferation repeat a second time in order to reach a productive antitumor response (Tester and Mora 2001).
One skilled in the art would, therefore, not expect immune therapy to be compatible with anticancer agents such as cytostatic agents that affect cell division. Immune therapy is expected to require cell division in the immune system, and cytostatic agents are known to affect or prevent cell division.
Therefore, prior to the advent of the instant invention, it was not expected to be possible to combine immunotherapy with anticancer agents, such as cytostatic or cytocidal drugs. Applicants understand that the present invention is the first time that effective use has been made of immunotherapy in the context of anticancer treatment, such as with cytostatic or cytotoxic drugs. As explained below, the inventors have discovered that not only is immunotherapy with superantigens compatible with anticancer agents such as cytostatic drugs, but in fact, coordinating the dosing of these two agents results in synergistic anticancer results. Furthermore, this combination therapy affords the benefit of reducing the production of antibodies in a treated person to the superantigens.